Conventionally, cases in which voltage to be applied from a power source drops or is not applied due to lighting or the like (instantaneous voltage drop) have been known. Particularly, with ships, there is a case where such instantaneous voltage drop occurs when an engine is turned on because a current instantly concentrates on a starter motor of the engine, and voltage is temporarily not applied to other electric components. The instantaneous voltage drop may also occur when the power source is switched from a ground power source into a power source in the ship (e.g., a battery connected to the engine). JP2000-116029A and JP1983-198116A disclose configurations of power source units in which voltage for electric components are maintained even when instantaneous voltage drop occurs.
JP2000-116029A discloses a backup power source unit including a backup battery in addition to an AC power source for normal use. With the backup power source unit, in a case of blackout, the battery applies voltage to electric components instead of the AC power source.
JP1983-198116A discloses a ship power source unit including a generator and various circuits that adjust an output voltage of the generator. The various circuits include an inverse conversion circuit that receives a predetermined gate signal and generates an alternation voltage. With the ship power source unit, when the output voltage of the generator is stopped, a capacitor disposed near the inverse conversion circuit supplies the gate signal to the inverse conversion circuit, instead of the generator.
However, since the battery in JP2000-116029A is only for backup, the battery needs to be disposed in addition to the normal power source unit. In this case, the size of the backup power source unit becomes large and the component cost increases. Moreover, since the capacitor in JP1983-198116A is also only for backup, it has similar problems.